Polymerized olefin synthetic lubricants



United States Patent Oflice 3,149,178 Patented Sept. 15, 1964 3,149,178 PGLYMERIZED OLEFIN SYNTHETIC LUBRICANTS Lyle A. Hamilton, Pitman, and Francis M. Seger, Mount Ephraim, N.J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York No Drawing. Filed Euiy 11, 1961, Ser. No. 123,126 Claims. (Cl. 260-6333) This invention relates to lubricants. It is more particularly concerned with improved synthetic lubricants for aircraft engines, and with the manufacture thereof.

As is well known to those familiar with the art, modern aircraft are designed to operate at high altitudes. This of course, gives rise to more severe requirements on the lubricating oils used in the engines. For example, the lubricant must have a relatively low pour point and a high viscosity index. It must also be responsive to chemical inhibitors and stabilizers.

In the case of jet turbine engines, an additional problem is encountered. Such engines are designed to operate at high temperatures. Accordingly, the lubricant must function and remain stable at temperatures in the order of 500 F. and higher.

It has been proposed to produce synthetic lubricants for special uses, such as in aircraft, by polymerizing alpha monoolefins thermally or catalytically in the presence of catalysts, such as di-tertiary alkyl peroxide and Friedel-Crafts catalysts, including boron trifiuoride and aluminum chloride. These lubricants have low pour points and high viscosity indices. They are, however, not sufliciently stable to high temperature lubrication conditions and are in some cases deficient in response to addition agents. When they are hydrogenated to increase stability by saturating olefinic double bonds, it has been found that the pour point is greatly increased and that the lubricants are still unstable at high temperatures.

It has now been found that novel highly effective saturated polymerized olefin synthetic lubricants can be produced simply and economically. It has been discovered that by removing the dimer portion of a polymerized alpha monoolefin prior to hydrogenation, a synthetic lubricant of low pour point and having good inhibitor response and high Viscosity Index is produced. It has also been discovered that by simple heat treatment, this synthetic lubricant can be rendered stable for high temperature lubrication.

Accordingly, it is a broad object of this invention to provide improved, novel synthetic lubricants. Another object is to provide hydrogenated, polymerized olefin synthetic lubricants of increased inhibitor response, high Viscosity Index (V.I.), and low pour point. A further object is to provide new hydrogenated, polymerized olefin synthetic lubricants that are thermally stable. A specific object is to provide hydrogenated synthetic lubricants produced from polymerized alpha monoolefins that have low pour points and high V.I. Another specific object is to provide new hydrogenated synthetic lubricants produced from polymerized alpha monoolefins that have been treated to render them thermally stable. A further spe cific object is to provide simple methods for producing the synthetic lubricants of this invention. Other objects and advantages of this invention will become apparent to those skilled in the art, from the following detailed description.

In general, this invention provides a novel synthetic lubricant having low pour point, high V.I., and good additive response and the method for producing it, which comprises distilling a polymerized normal alpha-monoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer; and completely saturating said residual fraction by hydrogenation.

The invention further provides a novel thermally stable synthetic lubricant and a method for producing it that comprises distilling a polymerized normal alpha-monoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer; completely saturating said residual fraction by hydrogenation; and heating the thus-saturated residual fraction at a temperature varying between about 600 F. and about 700 F., for a period of time varying inversely between about 1 and about 10 hours, with 650 F. for 3 hours being preferred.

In another embodiment, this invention provides a thermally stable synthetic lubricant and a method for producing it, that comprises distilling a polymerized normal alpha-monoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer; heating said residual fraction at a temperature varying between about 600 F. and about 700 F., for a period of time varying inversely between about 1 and about 10 hours; and completely saturating the thus-heated residual fraction by hydrogenation.

As used in the specification and claims, the term high V1. refers to Viscosity Indices of about and higher. The term polymerized normal alpha-monoolefin synthetic lubricant means synthetic lubricants made by polymerizing normal alpha-monoolefins (C to C either thermally or catalytically in the presence of a di-tertiary alkyl peroxide or of a Friedel-Crafts catalyst, including boron tri-fiuoride and aluminum chloride, under mild conditions. As contemplated herein the term excludes polymers produced in the presence of other peroxides, such as diacyl peroxides, which polymers contain structural elements of the peroxy catalyst. It has been found that polymers made in the presence of a di-tertiary alkyl peroxide do not contain structural elements of the peroxide catalyst. In this respect, the latter polymers are the substantial equivalent of thermally polymerized olefins. When Friedel-Crafts catalysts are used, polymerization conditions must be relatively mild.

In order to produce the synthetic lubricants of this invention that have high V.I., low pour points, and good inhibitor response, the selection of the normal alphamonoolefin monomer is important. The best, and particularly preferred monomer is l-decene. The l-decene can be relatively pure monomer or an olefin or hydrocarbon mixture rich in l-decene. It has also been found, however, that mixtures of normal alpha-monoolefins having between about 6 and about 12 carbon atoms can be used, provided that the mean value of the olefin chain length is about 10 carbon atoms. Thus, for example, a mixture of equal parts of l-hexene, 1- octene, l-decene, and l-dodecene produced a satisfactory lubricant in accordance with this invention.

The thermally polymerized olefins utilizable herein are described in United States Letters Patent No. 2,500,166. The polymerization is carried out generally at temperatures varying between about 500 F. and about 750 F. for periods of time varying between about 20 hours and about one hour. Preferably, the polymerization is carried out at temperatures varying between about 600 F. and about 700 F.; the optimum reaction times at the maximum and the minimum reaction temperatures being specified in the respective patent specifications.

In No. 2,500,166, the olefin reactants are normal alphamonoolefins having between 6 carbon atoms and 12 carbon atoms per molecule. The utilizable olefins are, for example, l-hexene, l-octene, l-nonene, l-decene, and 1- dodecene. The olefin reactant can be substantially pure normal alpha-monoolefins, mixtures of olefins and/or ens-9,1

. ly-available and especially preferred catalyst is di-tertiary butyl peroxide. The amount of peroxide catalyst used is bteween about 0.01 and about 0.3 mole per mole of normal alpha-monoolefin reactant. The temperature employed is the activation temperature of the peroxide catalyst and varies between about 100 C. (212 F.) and about 200 C. (392 F.). In general, the time of reaction varies between about one hour and about 6 hours.

Polymerized normal alpha-monoolefin oils utilizable in the present invention can readily be prepared in the presence of Friedel-Crafts catalysts, under relatively mild conditions. As is well known to those skilled in the art, severe operating conditions, particularly with. some promoted Friedel-Crafts catalysts, induce undeshable side reactions, isomerization, resinificaticn, etc. It is further rec- .ognized that all Friedel-Crafts catalysts are not entirely equivalent in the type of oils produced. To a great extent, the choice of catalyst and of reaction conditions can be made in order to produce polymer lubricants of a desired. viscosity. 7

Polymerization of l-decene (or its equivalent) with AlCl 'catalyst at temperatures below about 70 C. produces lubricating oils having a kinematic viscosity of 2545 centistolres at 210 F. In general, such oils are producedby gradually mixing olefin with 1-3 weight percent (based on total olefin charge) of AlCl over a period of 26 hours. A preferred procedure involves incrementaladdition of olefin to a slurry of catalyst in an inert hydrocarbon, e.g., n-heptane.

Polymerization of l-decene (or it equivalent) in the presence of AlCl at temperatures of 100200 C. gives oils of about 12 centistokes kinematic viscosity measured at 210 F. A feasible method of operation is to add AlCl rapidly to olefin, permitting the temperature to rise suddenly to 150 C. or higher. Under these conditions EXAMPLE 1 'A mixture of 3100 grams (22.14 moles) of I -decene and 160 grams (1.10 moles) of di-tertiary butyl peroxide was heated in a reaction vessel, at a temperature of 150 C. for 5 hours. The reaction product thus obtained was topped first at atmospheric pressure and later at 60mm. absolute pressure to remove unreacted l-decene. The residual polymer oil product had the properties set forth in polymerization occurs readily, to the extent that most of Table I. 7

EXAMPLE 2 The polymer oil product of Example 1 was hydrogenated to saturate the olefinic double bonds. genation was carried out by conventional procedures using an Aminco rocking bomb with nickel-on-kieselguhr catalyst (20 g. per g; of. oil). Initial hydrogen pressure was 1500 p.s.i.g. Temperature was held at 300 F. for

From the data in Table 1, it will be apparent that hydro genation of the polymer oil had no substantial effect upon the viscosity characteristics of the oil. On the other hand, the pour point was increased by about 100 F.

EXAMPLE 3 Portions of the synthetic lubricants defined in Examples 1 and 2 were blended with known oxidation inhibitors. Each blend Was subjected to the Laboratory Oxidation Test (B-IOA). Pertinent data on blends and test results are set forth in Table II.

In the Laboratory Oxidation Test (IE-10A), a 25-cc.-

sample of test oil is placed in a 200 x 25 mm, test tube, together with 15.6 sq. in. sandblasted iron wire, 0.78 sq. in. polished copper Wire, 0.87 sq. in. polished aluminum wire and 0.167 sq. in. polished lead surface. The tube is maintained at 325 F. in an aluminum block bath. Dry air is bubbled through the test oil for 24 hours, at a rate of 10 liters per hour. At the end of the test Table II Oil of Example 1 Oil of Example 2 Additives Percent Percent V N.N. 1s. Lead N.N. Vis. Lead Incr. Change, Sludge Loss, Incr. Change, Sludge Loss,

K.V. a mg. K.V. at mg. 100 F 100 F.

None .1 9. 9 1,000 Nil 21 8. 7 570 N'l g i ig ao sz m; Acryl 6i i17fi) 5.2 42 Nil 0. 49 6.8 Trac e "632 umazarm, ec .9 1 Nil 44.5 O OD 5(%l$1%; Quinazarin, o.i% (Re- 7 0 O 5 N11 crys 0.23 8.7 Nil Nil 0. 012 56%, yuAggrite Hi Par, 0.5%; 00 5 1 N11 cry 0i 9 l 1.8 17.5 Nil 8. 2 TricosylP.A.N., 1 6.9 232 N11 252 0 1 M1 Tr1cosylP.A.N., 10% 4. l 136 Nil 206 1. 1 V 34. 0 Hvy. 70. a

period there are noted and reported the increase in Neutralization Number (N.N.) (ASTM D974), the percent increase in viscosity measured at 100 F., the amount of sludge if any, and the milligrams loss in weight of the lead specimen.

The additives used in the blends reported in Table ll were commercially available oxidation inhibitors and stabilizers. Inhibitor 162 (du Pont) is a mixture of monoand di-lorol (C esters of orthophosphoric acid. Acryloid 7-94 is a polymethacrylate V.I. irnprover. OD. 561 is cadmium diamyldithiocarbamate. Agerite Hi Par is a mixture of phenyl-beta-naphthylamine, isopropoxydiphenylamine, and diphenyl paraphenylenediamine. Tricosyl P.A.N. is tricosyl phenyl-alphanaphthylamine. The additive formulations shown are typical of lubricating oil formulations.

From the data in Table II, it will be apparent that the hydrogenated synthetic lubricant has a greater response to inhibitors. As noted hereinbefore, however, this decided advantage is overshadowed by the unsatisfactory increase in pour point. In one aspect if this invention, the advantages of a hydrogenated synthetic lubricant and of low pour point are obtained by simple fractionation of the synthetic lubricant.

Surprisingly, and contrary to usual expectation, it has been found that it is the dimer portion of the polymerized normal alpha-monoolefin synthetic lubricant that induces a high pour point. Accordingly, a hydrogenated synthetic lubricant of low pour point is obtained by removing, by distillation, a fraction of the polymerized normal alphamonoolefin synthetic lubricant containing the dimer. The residue thus obtained is then hydrogenated to saturate olefinic double bonds. The dimer out can be recycled to the polymerization step, dong with fresh monomer feed. Alternatively, the same results can be obtained by first hydrogenating the polymerized olefin synthetic lubricant and then removing the dimer. This me hod, however, is less desirable, because the dimer is now saturated, in this case, and is not available for recycling to the polymerization step. Thus, if there is no use for the saturated dimer, it is a loss to the process.

The following example demonstrates a hydrogenation and topping operation of this invention when l-decene is used as the olefin charge.

EXAMPLE 4 Using the procedure described in Example 1, 3100 grams (22.14 moles) of l-decene were polymerized using 160 grams (1.10 moles) of di-tertiary-butyl peroxide catalyst. The polymerization was carried out at 150 C. for 5 hours. Unreacted l-decene was removed by distillation. The properties of the polymer oil thus obtained (designated Raw Polymer Oil) are essentially those of Example 1.

This polymer oil was subjected to distillation to remove a cut (consisting chiefly of dimer) boiling up to 180 C. under 1 mm. mercury pressure. The residual oil (designated Topped Polymer Oil) had the properties set forth in Table III.

The topped polymer oil Was saturated by hydrogenation in contact with nickel catalyst. The conditions used were the same as those of Example 2.

The product (designated Hydrogenated Topped Polymer Oil) had the properties set forth in Table III.

From the data in Table III, it will be noted that removal of the dimer fraction greatly lowered the pour point. Most significantly the pour point was still low, even after hydrogenation of the topped polymer oil.

As mentioned hereinbefore, the dimer can be removed either before or after hydrogenation. This point is illustrated by the following example.

EXAMPLE 5 A thermal polymer oil was prepared by heating 1337 grams (9.55 moles) of l-decene at a temperature of about 650 F. for 10 hours at maximum pressure p.s.i.g. The product Was topped to remove Unreacted l-decene, leaving a polymer oil. This oil was then subjected to distillation at about C. under 3 mm. mercury pressure to remove the decene dimer. The residue (designated Polymer Oil Less Dimer) had the properties set forth in Table IV.

This dimer-free polymer oil was hydrogenated over nickel catalyst under the usual conditions described in Example 2. The resultant oil (Dimenfree Hydrogenated Polymer Oil) had the properties set forth in Table IV. As the pour point was unsatisfactory, the hydrogenated polymer oil was further distilled up to a vapor temperature of 230 C. at l nun. mercury pressure, in order to remove decene dimer. The residual oil (Residual Hydrogenated Polymer Oil) had the properties set forth in Table IV.

Table IV Polymer Dimer-free Residual Oil Less Hydrogen- Hydrogen- Dimer ated Poly ated Polymer Oil mer Oil K.V. at 210 F cs 7.11 7. 39 9.18 K.V. at 100 F cs 41.17 43. 50 61. 16 V1 134 134 128 Four Point, 60 +10 0 API Gravity 36. 9 37. 7

1 Dimer removal found to be incomplete.

A reaction vessel was charged with 3000 g. l-decene and placed in a cooling bath. A total of 26 g. AlCl was added in small increments over a period of 95 minutes. During this period of time the temperature of the reaction mixture was 203-6 C. Then, the reaction mixture was filtered to remove solid catalyst. The filtrate was blown with ammonia gas to remove dissolved aluminum compounds and filtered. The blowing operation was repeated. The final filtrate was topped to remove unreacted monomer and subjected to distillation up to 132 C. at 0.5 millimeter mercury pressure to remove dimer. The remaining, residual polymer oil had the properties set forth in Table V.

EXAMPLE 7 A reaction vessel was charged with 300 g. of l-decene and 3 g. AlCl were added in one portion. The temperature of the reaction mixture rose from 26" C. to C. in four minutes. A water bath was applied to the reaction vessel to remove heat. After 40 minutes, the temperature was 80 C. The reactants were maintained at 80 C. for one hour. The raw product Was filtered to remove solid catalyst. The filtrate was Washed first with aqueous sodium hydroxide (5%) and then with '2 water and filtered. The product was topped to remove unreacted monomer and then dimer was removed by distilling to a temperature up to 210 C.,under l millimeter mercury pressure. The remaining polymer oil had the properties set forth in Table V.

EXAMPLE 8 ing polymer oil was further fractionated into a, fraction boiling at 200-222" C. at l millimeter mercury pressure. As is generally the case with B1 catalyzed polymer products, the trimer is an excellent synthetic lubricant, as Well as the residual oil product. The properties of the trimer cut and of the residual oil are set forth in Table V.

EXAMPLE 9 This example illustrates the preparation of polymer oil from a mixture of l-olefins averaging 10 carbon atoms. Into a reaction vessel .was placed a charge containing, by weight, 25 percent l-hexene, 25 percent l-octene, 25 percent l-decene, and 25 percent l-dodecene. Over a period of 3 hours 1.4 weight percent of a decanol-BF complex was added in two portions. The reaction temperature was between 5 C. and 29 C. The product was washed and filtered. Then, it was topped to remove monomer and distilled up to 190 C. at 0.4 millimeter mercury pressure to remove dimers; From the remaining oil was removed a heavy distillate (chiefly trimer) boiling at l90224 C. at 0.4 millimeter-mercury pressure. The properties of this distillate and of the residual polymer oil are set forth in Table V.

Table V Example N 6 7 8 9 Product Resid- Resid- Trimer Resid- Trimer Residual ual ual ual K.V. at 210 F., S1. 85 11.86 3.69 G. 83 2. 7 6.40 K.V. at 100 F., cs 290. 8 84. 84 16. 22 42. 30- 11.06 37. 93 V.I 126 128 131 125 102 127 Four Point, F- 55 -65 EXAMPLE 10 A polymer oil, prepared as described in Example 7, was hydrogenated using the procedure of Example 2. Pertinent properties of the hydrogenated polymer oil are set'forth in Table VI.

EXAMPLE 11 A composite of trimer and residual. polymer oil, prepared as in Example 8, was hydrogenated using the method of Example 2. Pertinent properties of the hydrogenated polymer oil are set forth in Table VI.

EXAMPLE 12 The combined polymer oil of Example 9 was hydrogenated using the procedure described in Example 2. Pertinent properties of the hydrogenated polymer oil are set forth in Table VI. a V i It has been mentioned hereinbefore that the synthetic lubricants produced herein are novel materials. These lubricants possess a plurality of properties not heretofor found in conventional mineral lubricating oils. For the ti? sake of comparison, included in Table VI are properties of two typical mineral lubricating oils. -Eoth oils were prepared from petroleum lube oil stocks by conventional solvent extraction, dewaxing, and percolation methods Oil A is from a paratfinic base stock. Oil B is from a naphthenic (Coastal) base stock.

Table VI Example No 10 11 12 011A on B K.V. at 210 F., cs 10. 52 4. 20 6.69 4.89 4. 00 K.V. at F., cs 73. as 20. 09 40. 74 28.02 22.4 v.1- 128 132 .107 70 Pour Point, F s5 -05 so +25 -20 Flash test, F 480 455 480 430 355 Fire test, F, 530 500 525 From the data in Table VI, it will be apparent that the synthetic lubricants of this invention have a community of desired properties, including high V.I., low pour point, and high Flash Point. These properties are not all evident in conventional petroleum lubricants. Thus, Oil A has a relatively high V.I. (although still 'less than but a high pour point. Oil B, on the other'hand, has a fairly low pour point (although still higher than -60 F), but a low V.I. In both cases, the Flash Points are lower.

The residual hydrogenated polymer oil products, aforedescribed, are excellent lubricants for many purposes. They also have excellent response to inhibitors. tionedhereinbefore, however, the requirements of high temperature jet engine lubrication are very severe. In such an application, the aforedescribed synthetic polymer oils are not sufliciently stable. In another embodiment of this invention the hydrogenated residual polymer oils can be rendered stable to high temperature operation by means of a simple thermal treatment.

The thermal treatment is carried out by heating the polymer oil at temperatures varying between about 600 F. and about 700 F. for a period of time varying inversely between about 1 hour and about 10 hours.

Preferred conditions are treatment at 650 F. for 3 hours.

Preferably, the polymer oil is agitated under nitrogen atmosphere during the thermal treatment. It has been found that the thermal treatment operation can be carried out of any point during the preparation of the final, heatstable synthetic polymer lubricant. Thus, for example, the following sequences of steps will produce stable lubricants:

(A) Polymerize l-olefin, remove dimer, hydrogenate, and heat treat; or

(B) Polymerize l-olefin, heat treat, remove dimer, and hydrogenate; or

(C) Polymerize l-olefin, remove dimer, heat treat, and hydrogenate.

It is preferable to complete the preparation of the poly mer oil with a hydrogenation step, even when sequence A is used. Thermal treatment usually will induce some cracking to olefins, and it is desirable'to saturate any olefinic bonds that may'form.

EXAMPLE 13 A raw olefinic polymer oil was prepared from l-decene, as described in Example 1. It was topped to remove dimer. The residual oil was then hydrogenated under the usual conditions (400 F, etc.). This material (Oil A) had the properties set forthin Table VII. A different lot of decene polymer oil was made in the manner of Oil A. It was then thermally treated by heating at about 645 F. for about 3 hours. Gas evolution occurred, agitating the liquid. The resultant oil (Oil B) had the properties given in Table VII. [This oil had been freed of volatile components 'by atmospheric-l-vacuum topp gs As men- Pour Point. F Flash test, Fire test, F Gr. API

EXAMPLE 14 A decene trimer oil, produced as in Example 8, was thermally treated by heating at about 650 F. for about 3 hours. The thus-treated oil was hydrogenated using the procedure described in Example 2. Pertinent properties of the hydrogenated treated oil are set forth in Table VH1.

EXAMPLE 15 A decene residual polymer oil, produced as in Example 8, was thermally treated by heating at about 650 F. for about 3 hours. The thus-treated oil was hydrogenated using the procedure described in Example 2. Pertinent properties of the hydrogenated treated oil are set forth in Table VIII.

EXAMPLE 16 A decene polymer oil, produced as in Example 6, was thermally treated by heating at about 650 F. for about 3 hours. The thus-treated oil was hydrogenated using the procedure described in Example 2. Pertinent properties of the hydrogenated treated oil are set forth in Table VIII.

From the data set forth in Table VIII, it will be apparent that the present invention provides heat-stabilized synthetic oils. By comparing their properties with those of Oil A and Oil B (Table Vi) it will be apparent to those skilled in the art that these new lubricants possess a community of properties not posessed by conventional petroleum base lubricating oils.

The thermal stability of lubricants utilizable in high temperature jet engine lubrication is determined in various ways. Several tentative methods have been employed. One consists of a cyclic exposure to heat as the oil is pumped over a spinning disc at elevated temperature.

Spinning Disc Test The basic test apparatus used herein to determine thermal stability is described in an American Society of Mechanical Engineers publication of a paper, The Oxidation of Lubricating Oils at High Temperatures, presented by A. L. Williams and E. A. Oberright at the ASME-ASLE Lubrication Conference, New York, New York, October 2022, 1959. The test apparatus was modified, in order to obtain a measurement of gas formation attributed to thermal degradation of the test oil.

In testing for thermal instability the oxygen reservoir was disconnected from the air circulating system. A U tube barometer was attached in its place. The circulating system was filled with nitrogen gas by thorough flushing. When the system reached test temperature oil was pumped into the disc. The system was balanced to atmospheric pressure and then again sealed. As the hot oil was pumped onto the hot disc the pressure rise from gas of decomposition was measured at regular 5 minute intervals.

Room temperature was kept constant by air conditioning to avoid pressure changes from room temperature changes.

In this test the spinning disc is rotated at 2500 rpm. The temperature of the disc is held at 525 F. In operation, oil is passed over the disc in a thin film, exposed to the high temperature. If the oil is degraded thermally a pressure rise in the manometer system will occur from the gases formed.

EXAMPLE 17 Oils A and B, as defined in Example 13, and in Table V, were each subjected to the spinning disc test. Pertinent results, in terms of millimeters pressure rise per hour were as follows:

Oil: Pressure rise, mm./hr. Oil A 72 Oil B 2 From the data in Example 17, it will be apparent that extremely heat stable lubricants have been produced by this embodiment of the invention.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

What is claimed is:

1. A process for producing a synthetic lubricant that comprises distilling a liquid polymerized normal alphamonoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer, and completely saturating said residual fraction by hydrogenation under catalytic hydrogenation conditions; said normal alpha-monooletin having between about 6 carbon atoms and about 12 carbon atoms and having a mean chain length of about 10 carbon atoms.

2. The process defined in claim 1, wherein said normal alpha-monoolefin is l-decene.

3. The process defined in claim 1, wherein said normal alpha-monoolefin is a mixture, by weight, of 25 percent l-hexene, 25 percent l-octene, 25 percent l-decene, and 25 percent l-dodecene.

4. A process for producing a synthetic lubricant that comprises distilling a liquid polymerized normal alphamonoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer, completely saturating said residual fraction by hydrogenation under catalytic hydrogenation conditions, and heating the thus-saturated residual fraction at a temperature varying between about 600 F. and about 700 F., for a period of time varying inversely between about 1 hour and about 10 hours; said normal alphamonoolefin having between about 6 carbon atoms and about 12 carbon atoms and having a mean chain length of about 10 carbon atoms.

5. The process defined in claim 4, wherein said normal alpha-monoolefin is l-decene.

6. A process for producing a synthetic lubricant that comprises distilling a liquid polymerized normal alphamonoolefin synthetic lubricant, thereby obtaining a fraction containing dimer and a residual fraction essentially free from dimer, heating said residual fraction at a temperature varying between about 600 F. and about 700 F., for a period of time varying inversely between about 1 hour and about 10 hours, and completely saturating the thus-heated residual fraction by hydrogenation under catalytic hydrogenation conditions; said normal alphamonoolefin having between about 6 carbon atoms and about 12 carbon atoms and having a mean chain length of about 10 carbon atoms.

7. The process defined in claim 6, wherein said normal alpha-monoolefin is l-decene.

l-hexene, 25 percent l-octene, 25 percent 1-decene,- and 25 percent l-dodecene.

References Cited in the file of this patent UNITED STATES PATENTS Reid Oct.

Seger et a1. Mar. 14, 1 950 Seger et a1. Mar. 14, 1950 Garwood Mar.'14, 1950 Shmidl Dec. 28, 1954 Garwood May 17, 1960 

1. A PROCESS FOR PRODUCING A SYNTHETIC LUBRICANT THAT COMPRISES DISTILLING A LIQUID POLYMERIZED NORMAL ALPHAMONOLEFIN SYNTHETIC LUBRICANT, THEREBY OBTAINING A FRACTION CONTTAINING DIMER AND A RESIDUAL FRACTION ESSENTIALLY FREE FROM DIMER, AND COMPLETELY SATURATING SAID RESIDUAL FRACTION OF HYDROGENATION UNDER CATALYTIC HYDROGENATION CONDITIONS; SAID NORMAL ALPHA-MONOOLEFIN HAVING BETWEEN ABOUT 6 CARBON ATOMS AND ABOUT 12 CARBON ATOMS AND HAVING A MEAN CHAIN LENGTH OF ABOUT 10 CARBON ATOMS. 